Barcelona - Where to stay with a family.

We are heading to Barcelona in Mrch and need to find a place to stay. We are looking at some vacation apartments and some hotels. We are a family of three, we have a toddler so we need a family friendly place. We are not sure whether we should book a place from here or should we book when we get there. Our first few days are covered as we are going with a team but we will be staying on after that. We are thinking of spending all our time in Barcelona with maybe a daytrip or two.
Any ideas????